The 10-speed bicycle is one of the most popular types in use today. It incorporates a set of five chain sprockets attached to the rear wheel and a pair of sprockets on the pedals, with a drive chain moved from one sprocket to another by means of a mechanism called a derailleur. Other similar types provide five speeds using a rear derailleur only; and twelve, fifteen, eighteen or twenty-one speeds using combinations of front and rear derailleurs. Of these, however, the ten speed is by far the most popular.
The derailleur mechanisms are controlled by cables actuated by control levers located within easy reach of the rider, and a speed change is effected by moving a control lever while continuing to pedal, causing the chain to be guided onto the desired sprocket by derailleur mechanism.
The process of making speed changes efficiently requires skill and patience, as the rider must remove his hand from the handlebar, move the lever, wait until the shift has been made, and then move the lever to a neutral position so that the chain does not rub the side of an adjacent sprocket. For an average rider this shifting process is complicated and annoying, and as a result he does not attempt to master the skill required to use all the speeds available. The average ten-speed bicycle is thus ridden like a five speed, with essentially all the shifting being done by the rear derailleur, and the front derailleur is shifted only when a hill is encountered. Accordingly, for an average rider it would be desirable to have a means for automatically shifting the rear derailleur so that only the front derailleur need be shifted in a conventional manner for hill climbing or descending.
Prior art attempts to provide automatic shifting of the rear derailleur have included devices which move the rear derailleur in response to changes in pedal pressure as sensed by the tension in the drive chain. Such prior art devices are generally complex and are designed so that the speed change takes place with varying degrees of pedal pressure, i.e., heavy pressure for shifting to lower gears and light pressure for shifting to higher gears. Shifting under heavy pedal pressure can cause damage to the chain and sprocket. In addition, unless a constant pedal pressure is maintained when no shift is desired, the device can cause unwanted gear changes. In actual use it is all but impossible for an average rider to maintain such constant pedal pressure, and such devices have not found wide acceptance.
Another drawback of prior art automatic shifting devices is that they do not prevail the rider to shift to a lower speed as the bike is coasting to a stop in anticipation of starting from a stop in a lower gear, which can be done with a conventional derailleur mechanism.
Because of the foregoing, it has now become desirable to develop a simple, foot-controlled shifting mechanism which can be adapted to any bicycle equipped with a derailleur speed change mechanism, to automatically effect a speed change when desired by the rider.